In the tax credits division of Revenue & Customs, the lowest paid employee earns about £15,000 and managers earn £22,000. The average pension is £5,500-£6,500 a year; hardly a king's ransom. Yet the government's pension reform proposals mean many staff will have much lower pensions when they retire. Take the junior manager who joined 22 years ago. She is expected to pay £60 extra a month and work seven years longer before she can retire, and yet her pension will be worth £5,200 less each year when she does retire aged 68. How is that justified?

Civil servants and Public and Commercial Services (PCS) union members are not averse to reform. Since 2006, new employees have been put on to a career average pension scheme, precisely to address affordability concerns. But these members will still be subject to the coalition government's proposals.

The government is wrong when it says reforming public service pension schemes is vital. It is also underestimating the outrage felt by hardworking civil servants, many of whom are low paid.

Here in the tax credits department, my members have been unhappy about the rate at which their pay has increased, but this was tempered by having a good pension. Over the years, we've had below-inflation pay rises (effectively a pay cut), significant reductions in the civil service redundancy scheme and, most recently, the introduction of a draconian attendance management scheme – the system by which Revenue & Customs manages sickness absence – which means disciplinary procedures could be started much more quickly. So the proposed pension changes are an attack on the last term and condition that's worth anything. My 120 members in tax credits here in St Helens, Merseyside, are very angry about that and as a result will be striking tomorrow.

The Hutton report said civil service pensions were sustainable, so these proposed changes are not about paying for the cost of our pension scheme but are being used to get more money into Treasury coffers to reduce the deficit.

There is a better and much fairer way. Some £120bn is lost annually in tax avoidance, evasion or is simply not collected at all. Revenue & Customs has cut 25,000 staff in recent years. This is a false economy. It should be investing in more staff. Each compliance officer brings in more than £658,000 in revenue. If this tax gap was closed, then there wouldn't be the need for these changes to our pensions and, more important, the draconian cuts to the public sector we're witnessing would become unnecessary.

It would also help to ensure that the services we provide don't suffer. In tax credits, employees are concerned about the quality of the service they are expected to provide, especially the proposed move to universal credit. My PCS members' ultimate aim is to provide a good service. With both the baby tax credit and the basic element of working tax credit being scrapped, they are worried that many households will suffer.

The removal of the basic element of tax credit will see many families £45 a month worse off, just when inflation has already eroded their standard of living. We need to ensure that our most vulnerable members of society are protected.

• Colette Smith is West Lancashire and West Cheshire PCS branch secretary. She was talking to Anna Bawden